Method and apparatus for identifying defects with ultrasonic echoes

ABSTRACT

A method and apparatus for ultrasonic fault testing using angled probe beams wherein the probes are mounted on movable guide bars thereby enabling the probes to be moved in any one, or all, of three dimensions. The movement of the probes is indicated by potentiometer output and recorded on a strip chart along with the reflected signals from the probes. The location of the flaw is derived by the ratio of voltages representative of the distance between the probe and a reference axis and the distance travelled by the ultrasonic beam.

ited States Patent Inventor Karl G. Walther Ilamden, Conn. Appl. No.872,473 Filed Nov. 24, 1969 Patented June 22, 1971 Assignee KrautiramerUltrasonics, Inc.

Stratford, Conn. Continuation of application Ser. No. 546,423, Apr. 29,1966.

METHOD AND APPARATUS FOR IDENTIFYING DEFECTS WITH ULTRASONIC ECHOES 8Claims, 11 Drawing Figs.

US. 73/673, 73/679 Int. Cl G0ln 29/04 Field of Search 73/677, 67.9

[56] References Cited UNITED STATES PATENTS 2,667,780 2/1954 VanValkenburg 73/679 2,846,875 8/1958 Grabendorfer 73/67.8 3,326,037 6/1967Stewart 73/67.8

OTHER REFERENCES Abrahams, C. J. Practical Industrial UltrasonicExamination, ULTRASONICS, Jan. Mar., 1965, p. 30- 35.

Primary Examiner-James J. Gill Assistant Examiner-John P. BeauchampAnomey-Watson, Cole, Grindle 8: Watson ABSTRACT: A method and apparatusfor ultrasonic fault testing using angled probe beams wherein the probesare mounted on movable guide bars thereby enabling the probes PATENTEDJUH22 12m SHEET 0F 4 AND FIGS

A D. CONVT FIGS) FICMO INVENTOR KARL (a. WALTHLR E ATTORNEYS METHOD ANDAPPARATUS FOR IDENTIFYING DEFECTS WITH ULTRASONIC ECHOES This is acontinuation of application Ser. No. 546,423, filed Apr. 29, 1966.

This invention relates generally to ultrasonic fault-testing equipmentand, more particularly, it relates to means for determining preciselythe location and nature of defects in metal objects such as plateshaving welds.

Ultrasonic flaw detection is well known in the art as shown by US. Pat.No. 2,280,226 to Firestone, and certain techniques are known to improvethis art, such as (1) techniques for angling a probing ultrasonic beamin US. Pat. No. 2,527,986 to Carlin, (2) techniques to transform theheight of echoes in a selected time interval into a signal voltage (U.S.Pat. No. 2,507,854 R. B. de Lano, Jr.), and (3) techniques forrecognizing the time interval between the transmitting pulse and defectecho represented by US. Pat. No. 2,494,990 to R. B. de Lano, Jr.

However, the prior art has essentially depended upon interpretation ofecho signals to determine dimensions and characteristics by skilledoperators after moving the probe positions and viewing the echodisplays, but has not provided for appropriate apparatus in suchultrasonic weld testers for accurately recording and determining boththe location and the nature of defects in such a manner that informationis developed precisely while being preserved so that any calculations orinterpretations contemporaneously made may be checked or analyzed at alater time. Such visual observations with human interpretation islimited generally to simple single dimensional analysis.

Accordingly, it is a general object of this invention to provideimproved automatic ultrasonic methods and testing equipment for locatingand identifying the characteristics of defects.

A more specific object of the invention is to provide ultrasonic testingequipment which permits analysis of defects by recording criticalrelationships between probe position and defect echoes so that both theposition and nature of the defects and indicated.

Another object of the invention is to provide automatic ultrasonictesting equipment for simplifying calculations of exact defect locationsin a body under test.

A further object of the invention is to provide ultrasonic testequipment and methods which provide nondestructive multidimensionalviewing of faults or defects in a body.

In accordance with this invention therefore, an ultrasonic testingsystem is provided with recording equipment which correlates defect echotime positiomduration and amplitude signals with probe position andattitude signals in such relationship that the exact nature of thedefect is readily calculated. This equipment maintains the ability ofthe skilled operator to survey the defect by moving the probe positionand attitude while observing defect echo response if desired but alsoprovides for a complete three dimensional analysis in a routine manner.

Simplified calculating methods are provided by the invention to permitidentification of defect positions by calculating a simple ratio of twodistances. This leads to simplified automatic equipment which can beextended to more comprehensive systems incorporating development ofrecorded signals identifying the defect shape and characteristics in twoor more dimensions.

Thus, the distance between an ultrasonic sending-receiving probe and theecho produced by ultrasonic techniques is measured as one parameteralong a time base of a cathode-ray tube, for example. A furthermeasurement is taken between the probe and a reference position or axis.A simple calculation of the ratio of these measurements then gives thelocation of the defect with respect to the reference position.

The position information thus developed may be recorded on a stripchart, for example, for future reference to check the calculatedposition or to analyze the characteristics of the defeet. In the latterrespect the defect position is scanned in at least one further dimensionto display the echo reaction and to develop a record of the response ofthe defect echo to the ultrasonic beam impinging upon it from differentdirections.

Details of the invention along with further features and objectives willbe found in the following specification which refers to the accompanyingdrawings, wherein:

FIGS. 1 and 3 are diagrammatic perspective views of an ultrasonicweld-testing device showing the manner in which defects are preciselylocated and identified in nature;

FIG. 2 is a sketch diagramming critical relationships in locating defectpositions;

FIGS. 4 and 5 are waveform charts of recordings typically produced inaccordance with this invention to display defect location and character;

FIGS. 6-8 are block diagrams of ultrasonic weld-testing embodiments ofseveral aspects of the invention;

FIG. 9 is a waveform diagram illustrating operation with the apparatusof FIG. 8; and

FIGS. 10 and 11 arediagrams of further specific apparatus embodimentsfor providing signal voltages useful in this invention.

The view of FIG. 1 illustrates certain principles and features of theinvention with reference to a typical body under observation to observedefects. The body comprises two plates 1a, lb welded together at a weldseam 2, which is to be observed along weld axis 2a for any defects suchas 7 occurring in the vicinity of the weld seam.

An ultrasonic probe'3 is positioned for sending and receiving ultrasonicsignals into the plate through an intermediate coupling medium such as aliquid interface, in a conventional manner. Echoes reflected back fromthe plate under inspection such as from defect 7 are processedconventionally in the flaw detector system 4 to provide a display 8 witha time axis indicating the distance between the transmitted pulse 9'andreceived echo 10. The probe 3 is oriented to direct an ultrasonic beaminto the plate at such an angle to the plate surface that the ultrasonicsignal beam enters index point A at a known angle 5 between a verticalaxis and the axis of the beam. The flaw detector system is of thegeneral type described for example, in the aforementioned patents andserves to produce a visible echo pattern on a cathode-ray tube (CRT) forexample, which relates the amplitude characteristics of the echo 10received by bouncing back from a defeet 7 in the path of the ultrasonicbeam along a reverse path.

In order to permit simple vertical scanning through the entire weld seamat a desirable beam angle with simple motion, an appropriate beam angleis selected with the beam path being reflected at the rear side of theplate la at point B to traverse the weld seam 2 and further reflect frompoint C after which the beam is dissipated in passing through plate 1b.A detectable portion of the energy is reflected from any defect 7encountered in the weld back through the same path B-A to probe 3, toproduce the echo display pulse 10 after a round trip' propagation timeto defect point 7 and back, which propagation time may be calibrated toread directly in distance to the defect on display 8. Thus, the transittime and distance are determinable in a conventional manner from knownsound velocity in the plate material.

If we first consider only the necessity to scan vertically through theentire weld seam 2 in the narrow section observed by the ultrasonicbeam, it may be seen that a back and forth movement of probe 3 willcause the beam axis portion B-C to move vertically through the entirecross section of the weld seam (or any equivalent designated zone of abody under test). Accordingly, the necessity is presented ofdetermining.

the exact position of the defect 7 with reference not only to verticalposition but also with reference to the lateral position in the zonebeing scanned. In this latter instance we can take as areferenceposition, the axis 2a of the weld seam foruse in calculating the exactlocation of the defect 7 in these two dimensions.

In calculating the defect location in accordance with the proceduresafiorded by this invention, it is necessary only to use two distances,one of which is distance AD between the beam entry position A and thereference axis point D, which in reality is simply known from theposition of probe 3. The other distance is the beam path A-B-7 knownfrom display b. When these two distances are known the simple ratioAD/A-B7 will provide a value calibratable to give the distance of thedefeet to either side of the center point D for the different scanneddistances A-D as the probe is oscillated back and forth.

A similar simple calculation may be made with the distance A-B, which isproportional to the thickness of the plate and thus the entire verticaldistance through the plate and the distance 8-7, which is proportionalto the vertical position of the defect in the plate. This may beaccomplished directly from the information available on the time axis ofdisplay 8 for example, by taking a reference position B (known fromangle and the thickness of the plate) from which the two distances A-Band 3-7 are determinable.

it is therefore possible by a simple process to determine the exactlocation of a defect in the two-dimensional sense by showing a verticalheight and lateral position. Simplified apparatus for automaticallydetermining these locations is described hereinafter.

in order to extend this measurement to a full three-dimensional display,it is only necessary to move the probe 3 along a progressive zigzag path6, which generally retains the weld seam 2 within beam region B-C alongthe entire depth of the plate extending along weld axis 2A. The distancealong axis 2a can be measured directly from the probe location on theplate.

These simple geometric calculations may be visualized from MG. 2, wherea plane indicated by lines 20 and 2b passes through the center of theweld, whose end at the edge of the plate is shown at 0. The ultrasonicbeam path A-B-C is shown intercepting defect 7, which is located Mlowsurface position D. The distance 14 indicates the location of the centerplane 2a-lb from the probe index point A, and the distance from the edgeof the plate 01) is designated l3.

Angle 112 between a plane 11 normal to the center plane of the weldthrough 2a and 2b may be termed the orbital scanning angle which is usedfor purposes later discussed. The length of the path A-B-7 can be readfrom the display 8. Since the thickness of the plate is known and theprobe angle 5, the calculation of defect position 7 for all threedimensions may follow in the preferred manner described or byalternative geometric calculations.

Also, the shape of the defect can be determined from the echo display ifthe position of the probe 3 is permitted to scan or rotate about thevertical axis of the defect 7 at various probe spacings lid to produce ascan pattern striking the defeet with the beam from differentdirections. The shape is then determinable by referral to the echoheight and shape. For example, a crack generates a maximum echoamplitude when the sound beam angle directly encounters its flat facenormally and the echo amplitude denotes defect size while a gas bubbleor spherical defect will exhibit the same echo amplitude from variousprobe positions.

Accordingly, this invention provides for a guiding harness forpositioning the probe as shown in FIGS. 3 and 6 to produce records suchas shown in FIGS. d and 5. This equipment provides for determining exactprobe position in a manner which can be correlated with echo shape sothat the aforegoing calculations of position of the defect and analysisof the defect shape can be made precisely and checked for accuracy froma permanent record displaying all necessary criteria.

Referring now to the apparatus signified in FIGS. 3 and 6 representativeof a preferred embodiment of the invention, it is seen that a flexibleprobe position is provided with position precisely designated at alltimes. Thus, a guiding rail i5 is mounted parallel to the weld seam axis2a, or other reference axis, by such means as clamping magnets 16a and16b. A cursor l7 rides on guiding rail T5 to traverse a path parallel tothe weld seam axis 2a, and has an extension arm providing pivot point Ddirectly over the weld axis 2a.

The position of the cursor along the axis is determinable as forexample, from an electrical voltage from source 34) as developed by amovable tap on potentiometer 1%, appropriately mechanically traversedacross its range as the cursor changes linear position. This voltage isrepresentative of the displacement l3 (FIGS. 2 and 4).

A probe-guiding bar H9 is pivoted about point D to permit movement ofthe probe 3 in an arc about the pivot point to supplement linear travelalong the guiding bar 19. Thus, a further potentiometer 20 has itsmovable tap mechanically coupled to indicate a voltage proportional tothe angle between the extended cursor arm and the guiding bar 19, andstill another potentiometer 22 has its movable tap mechanically coupledto denote the distance of probe 3 along the guiding bar 19. Thus, thecritical distances hereinbefore discussed are automatically developedfor appropriate use in making calculations by either analysis of thecharts of recorder 35 or by automatic computation in an analog computer.The mechanical positioning of all three otentiometers i8, 20, 22 bymovement of the probe position is indicated by dotted lines in MG. 6.

These variable voltages representative of probe position are directed toa conventional multiple-channel strip recorder 35 with known constantpaper feed to afford a time base to produce the permanent records shownin FIG. 4, where signals 23 and 2d are obtained from the flaw detectorand monitor system 4, and signals l2, l3, and 14 represent the voltagesfrom potentiometers 13, 20, and 22.

Preferably, the chart has calibrated amplitude coordinates (not shown)in the various channels. Thus, channel 13 will display the probedisplacement 13 along the axis corresponding to the distance 0-D in H6.2, as derived from potentiometer l8. Channel 14 gives the correspondingdistance A-D of the probe from the weld as derived from potentiometer22, and the angular rotation representative of the orbital scanningangle is designated in channel l2 as derived from potentiometer 2%.

The amplitude history of any echoes 10 is shown on trace 23, and trace24 is a derivative of the echo signal which denotes the width across thedefect. This latter signal is derived by sensing 50 percent amplitudepoints on the echo wavefonn and generating a resulting square wavesignal over the resulting time duration between the 50 percent amplitudepositions. Apparatus such as shown in FlG. 7 might be used, for example.

in this derivation system, the peak pulse amplitude is retained bycapacitor 30 so that half its amplitude appears at tap 31 on resistor32. When this coincides with either the rising or falling envelope ofthe echo delayed through delay line 33, then coincidence circuit 3d cancomplement flip-flop circuit 35 to change its state and thus generatethe square wave signals at output lead 24. Thus, normally trace 2 3 willbe offset somewhat from trace 23 because of the action of delay line 33.This delay should be at least half as long at the widest defect to bedisplayed.

The operation of this technique for determining defect width isnecessary because of a finite ultrasonic beam width. Thus, as a beambegins to scan a defect, the amplitude of the echo increases to one-halfits maximum amplitude until the beam axis reaches the edge of thedefect, and in the same way exceeds this amplitude until the beam axispasses the opposite edge. As the entire beam width is impinging upon thedefect therefore the amplitude is twice that at the edges. Thus, thesignal trace 2 3 developes an easily interpreted visual record of thewidth of the defect which aids in analysis of the defect shape andcharacteristics.

An operator when encountering a defect in region 25 after moving probe 3through a zigzag scanning pattern 6 of HG. ll, shown on trace M with asuperimposed cycling orbital scanning angle pattern shown on trace 12,may alter the probe movement pattern to develop signals on traces 23 and24 representative of the shape of the defect. in essence, the zigzagmotion (trace M) is stopped along with displacement (trace 13) while asingle orbital scanning cycle (trace 12) is effected over a longer timeinterval to permit echo signal amplitude history to be displayed ontrace 23.

It is readily seen that the display in FIG. 4 gives the exact locationof every defect indicated by an echo. The position either can becalculated by analog computing equipment or can be laid out on a graph.Furthermore, the width and amplitude of the echo display indicate theshape of the defect.

An additional indication of the record for monitoring performance of theequipment is desirable, and can be provided as shown in FIGS. 8 and 9.Normally a couplant such as an oil bath t) is used between theultrasonic probe 3 and the surface of plate I. It is desirable thereforeto monitor not only overall ultrasonic equipment performance but alsothe couplant operation, since the echo amplitude information ismeaningless ifthe equipment is not properly calibrated.

Accordingly, in FIG. 8 an additional probe 43 (or alternatively a changeof angle of probe 3) is used to project a sound pulse in beam path 44into the plate so that it reflects back and forth between the twosurfaces. This provides a relative amplitude between transmitted pulsereference 45 and succeeding echo pulses 46 of decreasing amplitude. Theequipment may be adjusted for a calibrated return echo on the basis ofthese known conditions with vertical probe 43 to compare with theamplitude of a defect echo l reproduced from angularly positioned probe3. This can be done on a test basis periodically or can be alternatelydisplayed by use of a multivibrator 47 which alternately gates therespective probes 43 and 3 in coincidence circuits 48, 49 for viewing incombined form through mixer 50 in the flaw detector apparatus 4. Amarker pulse 51 between the two traces may be developed through lead 52,if desired.

The defect position can be simply derived in accordance with the processafforded by this invention with an analog computation circuit such asshown in FIG. 10. Thus, by use of a simple balanced bridge in which bothRx and Ry are variable rather than the conventional use of only onevariable, the ratio of Rx/Ry will provide an indication on zero centermeter 65 identifying position of the defect. Calibration and choice ofresistance values is readily within the skill of those in theinstrumentation art employing bridges.

An indication of the flaw position hereinbefore described by use of theratio of distances A-D/A-B-7 can be produced with potentiometer 21 ofFIG. 3 being resistance Rx and with an additional potentiometermechanically linked to a pointer for scanning the time display 8 of theflaw detector 4 to serve as resistance Ry to display an equivalentdistance A-B-7. Then meter 65 would display the position of the flaw 7to the right or left of the centerline 2a of weld seam 2.

Using this technique a recording as displayed in FIG. can be developedto produce a three-dimensional picture of the echoes received.

In this display trace I denotes the traversal of the probe along thereference axis (2a). This trace is displayed in quantized form for readyreference with polarization to indicate direction of travel. Forexample, as shown in FIG. 11 the indication may be derived from cursorpotentiometer 18, through capacitor 66. Thus, positive and negativechanges are channeled through rectifiers 67, 68 to analog to digitalconverters 69, 70 to produce digital marker pulses of oppositepolarities, which may be combined in mixer circuit 71 for output on lead72 which will operate recorder channel I.

Traces II and III may be derived from ratio circuits such as in FIG. toproduce a plan view display of echoes where distance from thecenterlines Q. indicate position of the echoproducing defect and thedimensions of the echo indicate its height and width.

The dimension of the defects like a crack for instance can be derivedeither by the echo amplitude if there is a small flaw only, or by thepresence of echoes dependent on traces l and II. Trace I shows theposition in direction of reference axis to A and trace III indicates thedepth of an echo-producing flaw referred to the surface of the specimenas a plate for instance.

Trace IV is the rotation angle similar to trace 12 of FIG. 4 and trace Vis the echo amplitude similar to trace 23 of FIG. 4. It is seentherefore this display gives a full three-dimensional layout of thesearch pattern history and all echoes reproduced, so that not only areechoes analyzable but also the procedural operation in inspection ofeach echo is retained upon the record.

In some scanning patterns slight errors might be introduced which can beovercome in calibration devices such as nonlinear potentiometers or withcompensating calculations made to layout scales, etc. Thus, even if zonescanning in the object under survey were accomplished by a pivotableprobe, the method and apparatus of this invention would be useful withslight change.

It is also desirable at times when using the ratio techniques of thisinvention to use a simple offsetting technique to exaggerate significantsignal amplitudes. Thus, consider in FIG. 2 that the ratio A-D/A-B-7gives a small signal component when Al) and A-B are long. However, byselection of an index point at B, a ratio such as D-E/B-7 can be used togive a significantly larger component of ratio change or signalamplitude. This technique is particularly useful in displayinginformation from small defects on traces II and III of FIG. 5, forexample.

While there is described what is at present considered a preferredembodiment of this invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the invention and it is, therefore, the object of theappended claims to cover all such changes and modifications as fallwithin the true spirit and scope of the invention.

What I claim is:

I. A method for determining the positions of defects in a materialhaving known sound propagation velocity characteristics by means ofultrasonic pulses comprising the steps of:

l. generating ultrasonic pulses within said material along a path havinga predetermined acute angle with respect to a line normal to the surfaceof said material, said ultrasonic pulses are generated with anultrasonic pulse generator probe movable along a guide member, saidpulses also being transversely directed relative to a selected referenceaxis having a predetermined location along said material,

2. moving said ultrasonic pulse generator probe in a direction parallelto said reference axis and rotating said ultrasonic pulse generatorprobe in a plane horizontal to the surface of said material about apivoting point located on said guide member supporting the pulsegenerator probe,

. detecting pulses reflected from a flaw and determining the timeinterval between their entrance into said material and reflection fromsaid flaw,

4. deriving signals proportional to a reference displacement of theprobe generator from the reference axis from signals proportional to therelative position of the probe from the reference axis when the pivotedend of the guide member is positioned at a predetermined point withrespect to said reference axis and the angular position of the guidemember relative to said reference axis and detecting ultrasonic pulsesreflected from a flaw at said ultrasonic probe and deriving signalsproportional to said time intervals representing pulse path lengths tothe flaw,

5. calculating the lateral location of the flaw from the reference axisusing the signals in step 4.

2. A method according to claim I further comprising the step of furtherrotating said probe at selected spacings along said reference axis andmeasuring the amplitude of signals reflected from said flaw to determineits shape.

3. A method according to claim 2 further comprising the step ofrecording the signals obtained in step 3 along with signals representingsaid time intervals and the amplitude of signals reflected from saidflaw.

41. A method according to claim 1 further comprising the step ofcalibrating the reflected pulse energy with a reference sound beam.

5. Apparatus for determining the position of defects in a materialhaving known sound propagation velocity characteristics, comprising,

means for generating ultrasonic pulses within said material along a pathhaving a predetermined acute angle with respect to a line normal to thesurface of said material, means at the generating location for receivingpulses reflected from said material, said pulses also being transverselydirected relative to a selected reference axis having a predeterminedlocation along said material,

means for supporting said pulse-generating means to enable saidgenerating means to be moved along an axis parallel to said referenceaxis lying in a plane horizontal to said surface and along an axisintersecting said reference axis at different angles,

means for detecting movement of the pulse-generating means along saidparallel and intersecting axes and means for determining the angularrelationship between said intersecting and parallel axes and forgenerating signals proportional to such movement and angularrelationship to produce signals proportional to the distance between thereference axis and said pulse-generating means,

means for deriving signals proportional to the time interval between theentrance of said ultrasonic pulses in said material and the reception ofsaid pulses by said means for receiving, and

means for calculating the lateral location of the flaw from thereference axis from said derived signals and said proportional signals.

6. Apparatus according to claim 5 further comprising means for recordingsaid signals proportional to the movement of the pulse-generating means,the signals proportional to said angular relationship, and the signalsproportional to said time intervals.

7. Apparatus according to claim 6 further comprising means forcalibrating the reflected pulse signals with a reference sound beam.

8. Apparatus according to claim 5 wherein said means for supportingrotates said pulse-generating means at selected spacings along saidreference axis and said apparatus further comprises means for measuringthe amplitude of signals reflected from said flaw to determine itsshape.

1. A method for determining the positions of defects in a materialhaving known sound propagation velocity characteristics by means ofultrasonic pulses comprising the steps of:
 1. generating ultrasonicpulses within said material along a path having a predetermined acuteangle with respect to a line normal to the surface of said material,said ultrasonic pulses are generated with an ultrasonic pulse generatorprobe movable along a guide member, said pulses also being transverselydirected relative to a selected reference axis having a predeterminedlocation along said material,
 2. moving said ultrasonic pulse generatorprobe in a direction parallel to said reference axis and rotating saidultrasonic pulse generator probe in a plane horizontal to the surface ofsaid material about a pivoting point located on said guide membersupporting the pulse generator probe,
 3. detecting pulses reflected froma flaw and determining the time interval between their entrance intosaid material and reflection from said flaw,
 4. deriving signalsproportional to a reference displacement of the probe generator from thereference axis from signals proportional to the relative position of theprobe from the reference axis when the pivoted end of the guide memberis positioned at a predetermined point with respect to said referenceaxis and the angular position of the guide member relative to saidreference axis and detecting ultrasonic pulses reflected from a flaw atsaid ultrasonic probe and deriving signals proportional to said timeintervals representing pulse path lengths to the flaw,
 5. calculatingthe lateral location of the flaw from the reference axis using thesignals in step
 4. 2. moving said ultrasonic pulse generator probe in adirection parallel to said reference axis and rotating said ultrasonicpulse generator probe in a plane horizontal to the surface of saidmaterial about a pivoting point located on said guide member supportingthe pulse generator probe,
 2. A method according to claim 1 furthercomprising the step of further rotating said probe at selected spacingsalong said reference axis and measuring the amplitude of signalsreflected from said flaw to determine its shape.
 3. A method accordingto claim 2 further comprising the step of recording the signals obtainedin step 3 along with signals representing said time intervals and theamplitude of signals reflected from said flaw.
 3. detecting pulsesreflected from a flaw and determining the time interval between theirentrance into said material and reflection from said flaw,
 4. derivingsignals proportional to a reference displacement of the probe generatorfrom the reference axis from signals proportional to the relativeposition of the probe from the reference axis when the pivoted end ofthe guide member is positioned at a predetermined point with respect tosaid reference axis and the angular position of the guide memberrelative to said reference axis and detecting ultrasonic pulsesreflected from a flaw at said ultrasonic probe and deriving signalsproportional to said time intervals representing pulse path lengths tothe flaw,
 4. A method according to claim 1 further comprising the stepof calibrating the reflected pulse energy with a reference sound beam.5. calculating the lateral location of the flaw from the reference axisusing the signals in step
 4. 5. Apparatus for determining the positionof defects in a material having known sound propagation velocitycharacteristics, comprising, means for generating ultrasonic pulseswithin said material along a path having a predetermined acute anglewith respect to a line normal to the surface of said material, means atthe generating location for receiving pulses reflected from saidmaterial, said pulses also being transversely directed relative to aselected reference axis having a predetermined location along saidmaterial, means for supporting said pulse-generating means to enablesaid generating means to be moved along an axis parallel to saidreference axis lying in a plane horizontal to said surface and along anaxis intersecting said reference axis at different angles, means fordetecting movement of the pulse-generating means along said parallel andintersecting axes and means for determining the angular relationshipbetween said intersecting and parallel axes and for generating signalsproportional to such movement and angular relationship to producesignals proportional to the distance between the reference axis and saidpulse-generating means, means for deriving signals proportional to thetime interval between the entrance of said ultrasonic pulses in saidmaterial and the reception of said pulses by said means for receiving,and means for calculating the lateral location of the flaw from thereference axis from said derived Signals and said proportional signals.6. Apparatus according to claim 5 further comprising means for recordingsaid signals proportional to the movement of the pulse-generating means,the signals proportional to said angular relationship, and the signalsproportional to said time intervals.
 7. Apparatus according to claim 6further comprising means for calibrating the reflected pulse signalswith a reference sound beam.
 8. Apparatus according to claim 5 whereinsaid means for supporting rotates said pulse-generating means atselected spacings along said reference axis and said apparatus furthercomprises means for measuring the amplitude of signals reflected fromsaid flaw to determine its shape.